The present invention relates generally to the reaction that occurs between glucose and proteins, and more particularly to the inhibition by various aminoguanidine derivatives of the reaction of nonenzymatically glycosylated proteins leading to advanced glycosylation end products.
The reaction between glucose and proteins has been known for some time. Its earliest manifestation was in the appearance of brown pigments during the cooking of food, which was identified by Maillard in 1912, who observed that glucose or other reducing sugars react with amino acids to form adducts that undergo a series of dehydrations and rearrangements to form stable brown pigments. Maillard, C.R. Acad. Sci., 154, pp. 66-68, (1912).
In the years that followed the initial discovery by Maillard, food chemists studied the hypothesized reaction in detail and determined that stored and heat treated foods undergo nonenzymatic browning as a result of the reaction between glucose and the polypeptide chain, and that the proteins are resultingly cross-linked and correspondingly exhibit decreased bioavailability. Finot, P. A. (1982) in Modification of Proteins, eds, Feeney, R. E. and Whitaker, J. R., American Chemical Society, 198, pp. 91-124, Washington, D.C. At this point, it was determined that the pigments responsible for the development of the brown color that develops as a result of protein glycosylation possessed characteristic spectra and fluorescent properties. However, the chemical structure of the pigments had not been specifically elucidated.
The reaction between reducing sugars and food proteins discussed above was found in recent years to have its parallel in vivo. Thus, the nonenzymatic reaction between glucose and the free amino groups on proteins to yield the Amadori product, has been shown to occur with hemoglobin, wherein a rearrangement of the amino terminal of the beta-chain of hemoglobin by reaction with glucose, forms the adduct known as hemoglobin A.sub.1c. The reaction has also been found to occur with a variety of other body proteins, such as lens crystallins, collagen and nerve proteins. See, Bunn et al., Biochem Biophys. Res. Comm., 67, pp. 103-109 (1975); Koenig et al, J. Biol. Chem., 252, pp. 2992-2997 (1977); Monnier, and Cerami, A., in Maillard Reaction in Food and Nutrition ed. Waller, G. A., American Chemical Society, 215, pp. 431-448 (1983); and Monnier and Cerami, Clinics in Endocrinology and Metabolism, 11, pp. 431-452 (1982). Moreover, brown pigments with spectral and fluorescent properties similar to those of late-stage Maillard products have also been observed in vivo in association with several long-lived proteins, such as lens proteins and collagen from aged individuals. An age related linear increase in pigment was observed in human dura collagen between the ages of 20 to 90 years. See, Monnier, and Cerami, Science, 211, pp. 491-493 ( 1981); Monnier, and Cerami, Biochem. Biophys. Acta, 760, pp. 97-103 (1983); and, Monnier et al., "Accelerated Age-Related Browning of Human Collagen in Diabetes Mellitus", Proc. Nat. Acad. Sci., 81, pp. 583-587 (1984). Interestingly, the aging of collagen can be mimicked in vitro by the cross-linking induced by glucose; and the capture of other proteins and the formation of adducts by collagen, also noted, is theorized to occur by a cross-linking reaction, and is believed to account for the observed accumulation of albumin and antibodies in kidney basement membrane. See, Brownlee et al, J. Exp. Med., 158, pp. 1739-1744 (1983); and Kohn et al, Diabetes, 33, No. 1, pp. 57-59 (1984).
2-Furoyl-4(5)-2(furanyl)-1H-imidazole has been isolated from the acid hydrolysates of browned proteins and is believed to be a cross-linker from the nonenzymatic browning of proteins, Pongor et al., Proc. Natl. Acad. Sci. USA, 81, 2684 (1984), and U.S. Pat. No. 4,665,192, issued May 12, 1987, and entitled "Methods and Agents for Measuring Protein Aging".
Methods of inhibiting the Maillard reaction in vivo using aminoguanidine are known, Brownlee et al., Science, 232, 1629 (1986), and U.S. Pat. No. 4,758,583, issued Jul. 19, 1988, and entitled "Method and Agents for Inhibiting Protein Aging". In the food industry, sulfites were found years ago to inhibit the Maillard reaction and are commonly used in processed and stored foods. Recently, however, sulfites in food have been implicated in severe and even fatal reactions in asthmatics. As a consequence, the sulfite treatment of fresh fruits and vegetables has been banned. The mechanism for the allergic reaction is not known. A need thus exists for a suitable agent for the inhibition of nonenzymatic browning for use in processed and stored foods, as well as in various other pharmaceutical and diagnostic products.
Additionally, the discovery of a suitable agent for the inhibition of nonenzymatic cross-linking would provide a means of reducing or obviating the effects of protein aging, especially in such disease states as diabetes mellitus, etc.